The present invention relates to a seal assembly for sealing a rod or shaft relative to a gland or housing surrounding the rod. In particular, the invention relates to a split dual seal assembly for providing a seal between a rod and the gland.
Hydraulic and pneumatic systems usually convert fluid pressure to a linear force by applying the fluid pressure to one end of a cylindrical piston which slides axially in a mating bore. A piston rod extends from the piston or shaft out through at least one end of the bore and into a gland or housing. To avoid a loss of fluid and fluid pressure from the systems, a sealing system is necessary to provide a seal between the rod and the gland or housing and/or between the piston and the bore.
Conventional sealing systems can employ a number of annular elastomeric sealing elements disposed within a groove formed in the gland. The annular sealing elements are sized to provide interference between the sealing elements and the outer surface of the rod. The degree of interference provided preferably allows smooth axial movement of the rod through the sealing elements while concomitantly providing fluid sealing between the rod and the gland.
Such conventional sealing systems suffer from a number of deficiencies. In particular, the reciprocating movement of the rod can cause the seal elements to extrude through the clearance gap provided between the rod and the gland. In addition, as the seal elements wear, the amount of radial compressive force provided by the seal elements against the rod decreases, resulting in a corresponding decrease in the sealing effectiveness of the sealing elements. To compensate for such a decrease in the sealing efficacy, a number of conventional sealing systems provide an axial compression mechanism to adjust the axial pressure on the seal elements, thereby increasing the radial compressive force provided by the seal elements against the rod. Such occasional adjustments can be time-consuming and can increase the cost of maintenance.
In order to overcome the wear problem associated with elastomeric seal elements, some conventional sealing systems include an additional elastomeric positioning element to place the seal elements into sealing contact with the rod by exerting axial and/or radial compressive forces against the seal elements. Such conventional sealing systems, however, typically do not function properly in all operating conditions. For example, in pressure-reversal conditions in which the pressure in the normally high-pressure side of the hydraulic or pneumatic system drops below the pressure in the normally low-pressure side of the system, the additional elastomeric positioning element can be ineffective for placing the sealing elements into contact with the outer surface of the rod.
Further, in such sealing systems, the additional positioning element does not contact the rod, and thus, provides no sealing function. Since only the sealing elements contact the rod, there is no cooperative effect between the sealing elements and the positioning element for ensuring that the concentricity of the seal is maintained. Loss of concentricity can lead to leakage of fluid or gas. For example, in many applications, the rod can be subjected to radial forces that tend to distort concentric alignment of the rod. Such a distortion of the alignment of the rod can in turn distort the sealing surfaces that contact the rod, thereby causing the sealing edges of the seal elements to lose sealing engagement with the rod.
Another drawback of the prior art sealing system is the poor wear characteristics of the seal elements necessitate frequent monitoring and replacement or adjustment of the seal elements. Replacement and installation of the seal elements or other components of the seal system can require the complete breakdown of the hydraulic or pneumatic system to pass the annular components over the rod. The replacement and adjustment process can thus require frequent long periods of down time for the system associated with the seal system.
It is thus an object of the invention to provide a seal assembly having seal elements that maintain sealing contact with the rod throughout a wide range of operating conditions including pressure-reversal conditions.
It is another object of the invention to provide a seal assembly having seal elements that maintain sealing engagement with the rod without necessitating frequent monitoring, replacement, or adjustment of the seal assembly.
It is yet another object of the invention to provide a seal assembly having seal elements that resist extrusion into the clearance gap between the rod and the gland.
It is further another object of the invention to provide a seal assembly having split components that facilitate monitoring, installation and replacement of the seal assembly.
Other and more specific objects of this invention will in part be obvious and in part be evident from the drawings and description which follow.
These and other objects of the present invention are achieved by the dual seal assembly of the present invention for providing a seal between a reciprocating rod and the gland. The dual seal includes first and second axially adjacent annular seal elements. The first seal element is constructed of a material having a different hardness than the material forming the second seal element. The first and second seal elements each include a seal edge contacting the rod to provide a respective seal between the first and second seal elements and the rod. At least a portion of the first seal element and/or the second seal element engages the gland to form the seal between the rod and the gland.
In accordance with one aspect of the present invention, the first seal element is positioned axially inward from the second seal element and the hardness of the material forming the first seal element is less than the hardness of the material forming the second seal element. Preferably, the durometer hardness of the material forming the second seal element is approximately between 50 Shore A and 25 Shore D and the durometer hardness of the material forming the first seal element is approximately between 50 Shore A and 95 Shore A.
The difference in hardness of the materials forming the first and second seal elements provides a number of significant advantages. By varying the hardness of the materials forming the seal elements, the first seal element and the second seal element can be configured to provide different functions within the dual seal assembly and can cooperatively provide an effective fluid seal under a wide range of operating conditions. For example, the lower durometer hardness material forming the first seal element allows increased elastic radial deflection of the first seal element when the first seal element is axially compressed by fluid pressure during operation. The first seal element, thus, can translate axial compressive forces into an increased radial sealing force by radially deflecting in the direction of the rod and in the direction of the groove. Conversely, the increased durometer hardness of the second seal element allows the second seal element to resist elastic deformation during operation thereby maintaining the concentricity of the softer first seal element, inhibiting extrusion of the first seal element into the clearance gap between the rod and the gland, and allowing the dual seal to operate under reverse pressure conditions.
In accordance with an alternative embodiment of the present invention, at least one of the components of the dual seal assembly is split to facilitate installation, replacement, monitoring, or inspection of the dual seal assembly. In particular, the installation, replacement, and inspection of the split seal component of the dual seal assembly can be performed without necessitating the complete breakdown of the hydraulic and pneumatic system and without having to pass the seal component over an end of the rod. Preferably, the first annular seal element is split at an interface to form first and second interconnecting edges that interlock to inhibit separating of the seal element at the interface.